This invention is generally directed to photoresponsive imaging devices, and more specifically, the present invention is directed to improved layered photoresponsive, or photosensitive, imaging devices containing a substrate, a photogenerating layer, and a charge transport layer, wherein the photogenerating layer contains photogenerating pigments dispersed in a resinous binder composition comprised of a poly(hydroxyether). In one embodiment of the present invention, the photogenerating layer and the charge carrier transport layer can be dispersed in a resinous binder material comprised of poly(hydroxyethers), particularly those derived from diphenols. The photoresponsive devices of the present invention are useful as imaging members in electrostatographic imaging systems, particularly, xerographic imaging systems, wherein latent images are formed thereon, and made visible, for example, by developer compositions containing toner particles and carrier particles.
Electrostatographic imaging systems, which are well known, involve the formation and development of electrostatic latent images on the surface of photoconductive materials referred to in the art as photoreceptors, or photosensitive compositions. In these imaging systems, and in particular in xerography, the xerographic plate containing the photoconductive insulating layer is imaged by uniformly electrostatically charging its surface, followed by exposure to a pattern of activating electromagnetic radiation such as light, thereby selectively dissipating the charge in the illuminated areas of the photoconductive member causing a latent electrostatic image to be formed in the non-illuminated areas. This latent electrostatic image can then be developed with developer compositions containing toner particles and carrier particles, followed by subsequently transferring this image to a suitable substrate such as paper. Many known photoconductive members can be selected for incorporation into the electrostatographic imaging system including for example, photoconductive insulating materials deposited on conductive substrates, as well as those containing a thin barrier layer film of aluminum oxide situated between the substrate and the photoconductive composition. The barrier layer is primarily for the purpose of preventing charge injection from the substrate into the photoconductive layer subsequent to charging, as injection could adversely affect the electrical properties of the photoreceptor compositions involved.
Examples of photoconductive members include those comprised of inorganic materials and organic materials, layered devices comprised of inorganic or organic compositions, composite layered devices containing photoconductive substances dispersed in other materials, and the like. An example of one type of composite photoconductive layer used in xerography is described for example, in U.S. Pat. No. 3,121,006, wherein there is disclosed finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. In a commercial form, the photoconductive composition involved is comprised of a paper backing containing a coating thereon of a binder layer comprised of particles of zinc oxide uniformly dispersed therein. Useful binder materials disclosed include those which are incapable of transporting for any significant distance injected charge carriers generated by the photoconductive particles. Accordingly, as a result the photoconductive particles must be in substantially contiguous particle to particle contact throughout the layer for the purpose of permitting charge dissipation required for a cyclic operation. Thus, about 50 percent by volume of photoconductive particles, is usually necessary in order to obtain sufficient photoconductor particle to particle contact for rapid discharge. These high photoconductive concentrations can destroy the physical continuity of the resin particles, thus significantly reducing the mechanical strength of the binder layer.
Illustrative examples of specific binder materials disclosed in the No. '006 patent include, for example, polystyrene resins, silicone resins, acrylic and methacrylic ester polymers, polymerized ester derivatives of acrylic and alpha-acrylic acids, chlorinated rubber, vinyl polymers and copolymers, and cellulose esters.
Other known photoconductive compositions include amorphous selenium, halogen doped amorphous selenium substances, amorphous selenium alloys, including selenium arsenic, selenium tellurium, selenium arsenic antimony, halogen doped selenium alloys, wherein the halogen is a material such as chlorine, iodine, or fluorine, cadmium sulfide and the like. Generally, these photoconductive materials are deposited on suitable conductive substrates, and incorporated into xerographic imaging systems for use as imaging members.
Recently, there has been disclosed layered photoresponsive devices comprised of photogenerating layers and transport layers, deposited on conductive substrates as described, for example, in U.S. Pat. No. 4,265,990, and overcoated photoresponsive materials containing a hole injecting layer, a hole transport layer, a photogenerating layer, and a top coating of an insulating organic resin, as described, for example in U.S. Pat. No. 4,251,612. Examples of photogenerating layers disclosed in these patents include trigonal selenium and various phthalocyanines, while examples of hole transport layers include certain diamines dispersed in inactive polycarbonate resin materials. The disclosures of each of these patents, namely, U.S. Pat. Nos. 4,265,990 and 4,251,612 are totally incorporated herein by reference.
Additionally, there is disclosed in Belgium Pat. No. 763,540, an electrophotographic member having at least two electrically operative layers, the first layer comprising a photoconductive layer which is capable of photogenerating charge carriers, and injecting photogenerated holes into a continuous second active layer containing a transporting organic material. The organic material is substantially non-absorbing in the spectral region of intended use, however, it is active in that allows the injection of photogenerating holes from the photoconductive layer and allows these holes to be transported through the active layer.
Other representative patents disclosing layered photresponsive devices include U.S. Pat. Nos. 3,041,116, 4,115,116, 4,047,949 and 4,081,274.
While the above-described photoresponsive devices are suitable for their intended purposes, there continues to be a need for improved devices. Additionally, there is a need for improved photoresponsive devices wherein the photogenerating material and the charge transport material can be dispersed in substantially identical specific resinous binder materials. Further, there continues to be a need for improved photoresponsive devices wherein the inert resinous binder material selected, particularly for the photogenerating composition, can function as an adhesive material, thereby eliminating the need for a separate adhesive layer, the primary purpose of which is to bind the photogenerating layer to a conductive ground plane. Additionally, there continues to be a need for resinous binder compositions which can be laminated and/or solvent coated, which binder is flexible and not brittle. Also, there continues to be a need for inactive resinous binder compositions useful as the dispersing medium for the photogenerating material, and/or the charge transport material, which compositions are substantially inert and thus, do not create environmental hazzards as is the situation with regard to some prior art binder compositions.